The present invention relates to a magnetic recording medium and a manufacturing method thereof. In particular, the invention relates to a vertical magnetic recording medium with a vertical magnetic recording layer excellent in corrosion resistance, as well as a manufacturing method thereof.
Importance has been attached more and more to magnetic disk drives for use in storage devices such as large-scaled computers, work stations and personal computers year by year, and they have been developed in terms of larger capacity and reduced size. Increased density is indispensable for increasing the capacity and reducing the size of magnetic disk drives. However, existent longitudinal magnetic recording systems in which minute bar magnets are arranged in a plane on a track for recording involves a problem in that the read output is lowered with time due to thermal fluctuation in a super high density region. On the other hand, vertical magnetic recording systems in which minute bar magnets are arranged vertically on a track surface have been demanded for rapid commercialization of products as the recording system capable of overcoming the problem described above. Examples of the vertical magnetic recording media include granular vertical media and stacked type vertical media. The granular vertical media have a structure of separating magnetic particles by non-magnetic oxides and enable high-density recording through fine crystallization. The stacked type vertical media include extremely thin magnetic layers and non-magnetic layers each with a film thickness of from several A to several tens of A which are alternately deposited, thereby providing large vertical magnetic anisotropy inherent to the multi-layered structure as the whole films. The granular vertical medium sometimes adopted a layer constitution of forming an adhesion layer, a soft magnetic layer, an intermediate layer and a granular magnetic recording layer over a glass substrate or a rigid non-magnetic substrate formed by applying nickel-phosphor plating on aluminum. It is known that the granular magnetic recording layer generally tends to suffer from corrosion.
In a conventional magnetic recording medium manufactured by using a sputtering film formation technique by sputtering, a diamond-like carbon (DLC) protective film is disposed with an aim of protecting a magnetic film against sliding movement by a magnetic head. In addition, the film thickness of the protective film is extremely reduced as far as to 5 nm or less. When the thickness of the protective film is increased for the improvement of the corrosion resistance, this is not preferred since it hinders the improvement of density due to loss of spacing between the magnetic recording layer and the magnetic head. Further, a perfluoro polyether liquid lubricant is generally used on the protective film with an aim of reducing the friction between the magnetic head and the magnetic recording medium.
Patent Document 1 (Japanese Patent Laid-open No. 2003-27258) discloses a pretreatment before forming a protective film on a surface containing at least metal, in which high corrosion resistance can be obtained for the metal surface even when the protective film covering the metal surface is reduced in thickness, by applying a hydrogen treatment to the metal surface thereby removing passivation.